Transport Evidence of Weyl Orbit in Dirac Semimetal ZrSiSe*

Symmetry-protected Dirac semimetals show linear dispersion described by two copies of the Weyl equation.  At the surface of such a crystal, the broken translation symmetry creates topological surface states called Fermi arcs. These Fermi arcs result in a cyclotron motion known as Weyl orbits that connect Fermi arcs on top and bottom surfaces through the chiral bulk states, which can be apparent in Shubnikov-de Haas oscillations. Fast Fourier Transform of Shubnikov-de Haas oscillations in thin flakes of ZrSiSe, a nonsymmorphic Dirac semimetal, reveals the unexpected frequency of 140 T not related to any known surface (450 T) or bulk (220 T) Fermi surface. We show that this frequency has a 2D nature by providing angle dependence and thickness dependence of quantum oscillations. Angle dependence of the 140 T frequency follows cos^-1(θ), in contrast to bulk frequency, 220 T, which shows no change with angle. In addition, thickness dependence shows that the amplitude ratio of the 140 T to 220 T components exponentially increases by decreasing the thickness. In addition, we provide a comparison of phase analysis of the 140 T with 220 T frequency that points to different origins of these frequencies. We speculate this 140 T frequency could arise from Weyl orbit oscillations that would be consistent with a Fermi arc with a length of 0.08  °A^-1 in ZrSiSe.